Determine which of the following are subspaces of Mnn: (a) The set of all lower triangular matrices. (b) The set of all n x n matrices A such that AT=-A. (c) The set of all n x n matrices A such that det(A)≠0. (d) The set of all n x n matrices A such that tr(A)≠0. (e) The set of all n x n invertible matrices. (f) The set of all n x n matrices A such that AB-BA for some fixed n x n matrix B.
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Let A and B be two lower triangular matrices. Then, their sum (A+B) is also a lower triangular matrix, and for any scalar k, the matrix kA is also lower triangular. Show more…
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Determine which of the following are subspaces of Mnn: (a) The set of all upper triangular matrices. (b) The set of all n x n matrices A such that det(A)=0. (c) The set of all n x n matrices A such that tr(A)=0. (d) The set of all n x n matrices A such that AT=-A. (e) The set of all n x n matrices A for which Ax=0 has only the trivial solution. (f) The set of all n x n matrices A such that AB=BA for some fixed n x n matrix B.
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